The overall objective of this project is to identify novel biomarkers of radio-sensitivity that will identify subsets of prostate cancer patients for which radiotherapy should be contraindicated. These novel biomarkers will subsequently be packaged in a robust, validated, sensitive and specific single nucleotide polymorphism (SNP)-based assay practical for use in the clinical setting. This assay will be capable of predicting the risk of developing adverse effects ? principally urinary morbidity and rectal injury ? resulting from radiotherapy treatment of prostate cancer. Through previous studies we have identified SNPs in multiple cohorts that are strongly associated with adverse effects resulting from radiotherapy. The goal of the current project is to validate these SNPs and discover new SNPs using multiple, independent cohorts and to initiate design of a multiplex assay to detect predictive SNPs.